Single-cycle strong terahertz pulse generation from a vacuum-plasma interface driven by intense laser pulses

Single-cycle strong terahertz pulses can be generated by irradiating ultrashort intense laser pulses onto a tenuous plasma slab. At the plasma surface, laser ponderomotive force accelerates electrons and induces net currents, which radiate terahertz pulses. Our theoretical model suggests that if tau(L)>2 pi/omega(p), with tau(L) as the laser-pulse duration and omega(p) as the plasma frequency, the emission frequency is around tau(-1)(L). On the other hand, the emission frequency is around omega(p)/2 pi if tau(L)< 2 pi/omega(p). Our numerical simulations support the theoretical model, showing that such a terahertz source is capable of providing megawatt power, field strengths of MV/cm, and broad frequency tunability.